Osmium Di-ammine Hydroxide, OsO(NH₃)₂(OH)₂

Osmium Di-ammine Hydroxide, OsO(NH₃)₂(OH)₂, results when the tetroxide is dissolved in concentrated aqueous ammonia and heated in a closed vessel to 50° C. On opening the vessel and evaporating the excess of ammonia, osmosammine hydroxide is obtained as a dark brown powder. It unites with acids to form salts, and upon being heated readily decomposes. When boiled with alkalies ammonia is evolved and hydrated osmium dioxide remains.

The most important salt is the chloride, which yields brown crystals which are decomposed by water, giving a basic salt.